1. Field of the Invention
The present invention relates to a wire electric discharge machine, and in particular, to a wire electric discharge machine having a function of adjusting a movement command of a movable axis and a threshold value of an abnormal load level in accordance with the state of the movable axis and the state of an environment in which the machine is placed.
2. Description of the Related Art
When a wire electric discharge machine is used, there are cases where an erroneous operation of an operator leads to collision of a wire guide section with a workpiece or a jig for fixing the workpiece. Japanese Patent Application Laid-open No. 2007-72879, for example, discloses a technique to cope with such cases through monitoring a load amount of a movable axis and preventing damage to a mechanical section of the movable axis, e.g. a wire guide section, by stopping the movable axis by an alarm stop in the case where the load amount reaches a set threshold value (see FIG. 8).
However, the wire guide section of the wire electric discharge machine is usually formed of a material that is damaged relatively easily, such as plastic, and hence, even when the technique disclosed in Japanese Patent Application Laid-open No. 2007-72879 is used, if the threshold value is set to a large value, the mechanical section may become damaged before the movable axis is stopped by the alarm stop, as shown in FIG. 9. On the other hand, when the threshold value is set to a small value with the intention to stop the movable axis by the alarm stop before the mechanical section is damaged, the alarm stop is activated due to even a slight load fluctuation in normal operation, leading to deterioration in operability.
In general, axial loading is high in the case where the viscosity of a lubricant is high in a low temperature state, and the axial loading is low in the case where the viscosity of the lubricant is low in a high temperature state. Meanwhile, axial loading is low in the case where an axial movement is performed at a low speed and the axial loading is high in the case where the axial movement is performed at a high speed, and this is especially conspicuous at the start of the axial movement. As shown in FIG. 10, in the case where the axial movement is performed in the low temperature state, the axial loading suddenly increases and the alarm is issued when the axial movement is performed at a highspeed from the start. However, as shown in FIG. 11, when the axial movement is started at a low speed in the beginning and the lubricant is applied for softening, then even in the case where the axis is moved subsequently at a high speed, the axial loading does not increase suddenly and the alarm is not issued. Application of the lubricant is, nevertheless, troublesome for an operator during preparation work, and again, deteriorates operability.
As described above, in the case where the axial movement is stopped by the alarm stop, it is necessary to set the threshold value of the alarm stop to a proper value and adjust a movement command of the movable axis in accordance with the state of the environment, and these operations are problematic in that they impose a considerably heavy burden on the operator.